Sensitivity study on streaming electrification of transformer liquids by using rotating disc method

Insulating liquids used in power transformers with forced liquid cooling systems could lead to the occurrence of streaming electrification phenomenon, which is a potential hazard to the operation of the equipment. In this study, a rotating disc system was built up in the laboratory so as to study the streaming electrification phenomenon occurred at different insulating liquid-pressboard interfaces under various conditions. The procedure for a single measurement was determined first based on the short-time characteristics of the current waveform. Then a 24-hour continuous measurement was carried out to investigate the long-time characteristics. The recorded waveforms indicated that a short-duration measurement is suitable for assessing the streaming electrification behaviour at a liquid-solid interface. The repeatability of measurements of the same sample in successive four days and the sensitivity of measurements to changing pressboard samples were also evaluated. Results indicated that changing pressboard samples leads to a relatively larger variation. The streaming electrification behaviours of a synthetic ester liquid and a mineral oil were compared. Preliminary results indicated that the synthetic ester liquid tends to generate higher streaming currents than the mineral oil.